Various polyurethane prepolymer compositions have long been used for soil consolidation and as grouts for sealing structures. U.S. Pat. No. 3,985,688 to Speech is directed to a foam polyurethane grout that is typically pumped into a sewer line by using a sewer packer device that is pulled through the sewer with cables. The sewer packer is stopped at each joint and inflated to form a seal on opposite sides of the joint. The grout is injected at the middle portion of the packer to seal the joint and, after cure of the grout, the packer is deflated and pulled to the next joint. Foam grouts are usually difficult to utilize in this type of packer, because the foam expands in volume more than about 100% during reaction of the prepolymer with water. This amount of expansion can cause the foam to back up excessively into the packer and trap it in the sewer line.
Other polyurethane prepolymer compositions, such as disclosed in U.S. Pat. No. 3,719,050 to Asao et. al, are gels and do not expand in volume more than about 50% during the reaction of the prepolymer with water. The Asao composition suffers from the disadvantage that in order to provide a good gel as desired, the prepolymer is reacted with water at an eight or nine parts water to one part prepolymer ratio. This ratio of reactants necessitates the use of specialized pumping equipment to apply this particular grout product.
The prior grout compositions discussed above were all provided as a prepolymer solution in water-miscible solvents, apparently because it was believed that water immiscible solvents would not mix well with water in the reaction step and would result in poor grouts.
A chemical soil consolidation composition utilizing a water immiscible solvent is "Scotch-Seal 5620" Chemical Grout, commercially available from 3M Company, St. Paul, MN. This composition has a high initial viscosity (about 6,000 centipoise), but has a low viscosity when mixed with water at about a 10:1 to 20:1 water/composition ratio to allow good soil penetration. Because of the high initial viscosity, this composition is not easily pumpable through standard grout pumping equipment and thus cannot be used as a sewer grout. This composition is an 80% polyurethane prepolymer in butyl benzyl phthalate.
An alternative composition employed as a sewer sealing composition is based on acrylamide, which is typically provided as a liquid pumped in a 1:1 ratio with water into the site of the leak and into the surrounding soil to form a cured gel which inhibits or prevents leaking. Much of the sewer sealing equipment employed in the United States and other countries has been designed to utilize acrylamide or acrylate type sealing compositions, that are pumped in a 1:1 ratio with water for cure.